Rectifying system for protecting inter-
nal combustion engines having plural
magnetos



Oct. 11, 1966 s. FRAKES ETAL 3,278,803

RECTIFYING SYSTEM FOR PROTECTING INTERNAL COMBUSTION ENGINES HAVING PLURAL MAGNETOS Filed Feb. 26, 1965 Q %I fl INVENTORS. "'1 F- 5/0 F24 K5 5 i JAM 5 M EAR/V156 \U Q Q BY ATTORNEYS.

United States Patent RECTIFYING SYSTEM FOR PROTECTING INTER- NAL COMBUSTION ENGINES HAVING PlLURAL MAGNETOS Sidney Frakes, Houston, Tex., and James W. Barnes,

Tulsa, Okla, assignors to Frank W. Murphy Manufacturer, Inc., Tulsa, Okla, a corporation of Oklahoma Filed Feb. 26, 1965, Ser. No. 435,653 8 Claims. (Cl. 317-18) The present invention relates generally to systems for deactivating magnetos of internal combustion engines in response to engine malfunction and, more particularly, to a system wherein plural magnetos feed the deactivating means via blocking recti-fiers, and constitutes a continuation-in-part of our copending application Ser. No. 64,804, filed Oct. 25, 1960, entitled Protective System for Internal Combustion Engines.

In high performance internal combustion engine systems, it is the practice to employ plural magnetos for supplying high voltages necessary to fire spark plugs. In engines having a large number of cylinders, spark plugs are arranged in groups, whereby a first magneto drives one group of spark plugs, a second magneto drives the spark plugs in a second group and so on. Other engines have two spark plugs per cylinder; the different plugs in each cylinder being driven by a separate magneto in parallel with the plugs in other cylinders.

It is known that engine systems of the type described can be protected from possible self destruction in the event of malfunction, such as low oil pressure or high temperature, by connecting a condition responsive switch and relay activating coil across the output winding of one magneto. The relay coil controls normally open circuited contacts, each of which is connected across the output winding of a separate magneto. in the event of malfunction, the condition responsive switch closes, energizing the relay coil, whereby all the contacts close to short circuit the magneto output voltage. Since the voltage that .the magneto can deliver to the spark plugs with its output winding short cir-cuited is insuflicient to cause ignition of the spark plugs, the entire engine system stops operating.

A defect in the prior art system is that failure of the magneto supplying current to the relay coil prevents actuation of the coil. Thus, if the magneto having its output winding in series with the relay coil should malfunction or if the shaft of the internal combustion engine driving the magneto that powers the relay coil is not rotating, the coil receives no current and closing of the condition responsive switch is ineffective to short circuit the remaining magneto. In such an event, one magneto continues to run to provide sufiicient voltage for enabling the engine to operate after the malfunction occurs. 1f the malfunction is to the lubrication or cooling system, continued subsequent operation of the engine system will very possibly result in self destruction thereof.

To one unfamiliar with the problems involved, it may appear that the solution to this problem res-ides in connecting all of the magnetos in parallel to the relay activating coil. In practice, however, this solution is impossible since the output voltages of the several magnetos are never in phase. Because of the phase divergence of the voltages deriving from the several magnetos, their peak positive voltages do not occur simultaneously. Hence, if the magneto output voltages are linearly combined, as would result if the magnetos were directly connected, the combined voltage reflected back to the magnetos would result in a magneto output less than the voltage necessary to achieve ignition. In consequence, the entire internal combustion engine system would be inoperative.

3,278,803 Patented Get. 11, 1966 According to the present invention, the problem is solved by connecting each magneto to the relay activating coil via a separate diode network. Each diode is poled to pass unidirectional pulses from its respective magneto to the coil while preventing current from the other magneto being coupled to the plugs of the group activated.

by the particular magneto. Thus, a cessation of the output voltage deriving from any particular magneto does not prevent activation of the relay activating coil. In addition, several magnetos are decoupled from each other whereby the out of phase relationships of their voltages does not influence spark plug firing of the several groups.

Because of the extremely severe transients that occur in a magneto driving system when spark plug ignition occurs, some type of protection must be provided for the diodes in the circuit. If the diodes are not protected, their back bias breakdown voltage is exceeded and they will be destroyed. We have found that a relatively simple network including a resistance and capacitance in parallel serves to damp the transient that occurs in response to spark plug ignition. After considerable experimentation, it has been found that optimum values of the resistance and capacitor are on the order of 1500 ohms and 0.01 microfarad, respectively.

A further feature of the invention is that only power from the magnetos is necessary to operate the relay activating coil. In many internal combustion engine systems, there is no source of electrical power readily available other than that deriving from the magnetos. Thus, to provide a unit that can be applied to any internal combustion engine system it is necessary to employ a coil activatin g network responsive to the magneto output voltage.

It is, accordingly, an object of the present invention to provide a new and improved system for deactivating an internal combustion engine system in response to a malfunction.

'It is another object of the present invention to provide a new and improved system for deactivating all of the magnetos in a plural magneto internal combustion engine system in response to malfunction occurring in the system.

A further object of the present invention is to provide a new and improved system for disabling each of the magnetos of an internal combustion engine system having plural magnetos when a system malfunction occurs.

it is still a further object of the present invention to provide a new and improved system for reducing to zero the output voltages of several magnetos in an internal combustion system in response to a malfunction of the system.

It is another object of the present invention to provide a system for activating a relay coil in response to the output voltages of several magnetos in a plural magneto internal combustion engine system, which coil, when activated, is effective to short circuit each of the magnetos in response to an engine system malfunction.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawing, wherein:

The single figure of the drawing is a circuit diagram of a preferred embodiment of the invention.

Reference is noW made specifically to the single figure of the drawing wherein magnetos 11 and 12 are driven through couplings 13 and 14 and shafts 15 and 16, respectively, from drive shaft 17 of an internal combustion engine. Magnetos 11 and 12 include the usual low voltage primary and secondary windings, permanent magnet secured to shafts 15 and 16, in combination with a distributor block and interrupter points. Each of magnetos 11 and 12 includes six output leads for delivering high voltage ignition potential to spark plug groups 18 and 19, respectively. Spark plug groups 18 and 19 form the two pairs of spark plugs in a V-12 engine, in the particularly disclosed embodiment. As is well known, spark plugs in groups 18 and 19 are sequentially activated in response to the high voltage pulses deriving from magnetos 11 and 12 to cause ignition, whereby the internal combustion engine is driven.

In addition to the high voltage output leads supplying voltages to the spark plugs in groups 18 and 19, low voltage A.C. outputs are derived from magnetos 11 and 12 on leads 21 and 22. The voltages on leads 21 and 22 are always out of phase with each other; in the specific internal combustion engine illustrated, they are 180 out of phase from each other.

The A.C. voltages deriving from the primaries of magnetos 11 and 12, on leads 21 and 22, are supplied to contacts 23 and 24, respectively, of latched relay 25. A further contact 26 of relay 25 is grounded and the relay is arranged whereby contacts 23, 24 and 26 are normally open circuited relative to each other. The latching mechanism for relay 25 includes electrically insulated toggle 27 having a tab 28 that holds armature 23 into engagement with contacts 24 and 26 once the relay has been activated. To unlatch the relay, toggle 27 is rotated by depressing spring 29.

The actuator for armature 23 comprises coil 31 that is driven by each of magnetos 21 and 22 through rectifying networks 32 and 33. Each of rectifying networks 32 and 33 comprises a diode 34 that is shunted by the combination of resistance 35 and capacitor 36. Diodes 34 of networks 32 and 33 are poled so that current of only the same polarity is supplied from the magnetos 11 and 12 to coil 31. The values of resistance 35 and capacitor 36 are selected to be approximately 1.5K ohms and 0.01 microfarad, respectively, so that the reversed voltages developed across diodes 34 are not excessive when the severe transients in the voltages on leads 21 and 22 occur at the time of spark plug ignition.

Connected to the end of coil 31 opposite from networks 32 and 33 are condition responsive switches 37 and 38, which are connected in parallel with each other and manually activated, normally open switch 39 to ground. Normally open switches 37 and 38, in the specifically illustrated embodiment, are responsive to water temperature and oil pressure within the internal combustion engine. Switches 37 and 38 are respectively closed when the water temperature exceeds a predetermined value and the oil pressure drops below a predetermined value, respectively.

In operation, under normal conditions, magnetos 11 and 12 supply igniting voltages to the spark plugs in groups 18 and 19 to drive the internal combustion motor shaft 17. In response to rotation of shaft 17, shafts 15 and 16 are driven, whereby A.C. output voltages are derived from magnetos 11 and 12 on leads 21 and 22. The voltages on leads 21 and 22 are 180 out of phase with each other so that during one-half cycle the voltage on lead 22 is positive, while the voltage on lead 21 is negative. On alternate positive half cycles of the voltage applied to lead 21, rectifier 34 conducts. Thereby, positive voltage is always being supplied to coil 31 through networks 32 and 33.

Because of the manner in which diodes 34 of network 32 and 33 are poled, substantially no current from lead 22 is coupled into magneto 11 via lead 21, and vice versa. This may be seen by considering the action of rectifier-s 34 in networks 32 and 33 at any particular time instant; assumed for illustration to be such that the voltage on lead 21 is positive While that on lead 22 is negative to ground. With a positive voltage on lead 21, current flows from the anode to the cathode of diode 34 of network 32 but is blocked by the diode in network 33 because the voltage on lead 22 back biases that diode. The impedances of resistor 35 and capacitor 36 in network 33 are sufiiciently large relative to the impedances of the internal magneto networks connected to leads 21 and 22 so that the two leads may be considered as decoupled from each other. On the following half cycle, when the voltage of lead 22 is positive relative to the voltage on lead 21, positive current flows through the anode cathode path of the diode 34 in network 33 but is blocked by the diode in network 32. Blocking occurs because of the relatively large diode impedance resulting from back biasing by the negative voltage on lead 21.

In the event of a malfunction due to excessive water temperature or reduced oil pressure in the internal combustion engine, one of switches 37 or 38 is closed, whereby coil 31 is activated in response to the DC. current applied thereto from magnetos 11 and 12. Even if only one of the magnetos 11 and 12 is functioning, to produce an output voltage on only one of leads 21 or 22, coil 31 exerts sufficient force on armature 23 to force the armature into the latched position whereby it engages tab 28. When coil 31 is activated, armature 23 is closed against contacts 24 and 26 so that the magneto output voltages on leads 21 and 22 are short circuited to ground. Short circuiting leads 21 and 22 to ground prevents the generation by magnetos 11 and 12 of voltages necessary to ignite the spark plugs in groups 18 and 19. In consequence, the internal combustion engine ceases to operate, drive shaft 17 stops rotating and any possibility of magnetos 11 and 12 deriving output voltages is prevented.

Upon cessation of the malfunction that caused contacts 37 or 38 to be closed automatically or which prompted an operator to close contact 39 manually, the circuit for coil 31 to ground is open. Since the malfunction can sometimes seemingly be cured when the engine stops running, it is necessary to provide the latching feature of relay 25 so that the magnetos can not thereafter be activated until the malfunction has been corrected. Only after the malfunction has actually been repaired is spring 29 depressed so magnetos 11 and 12 are able to derive voltages sufiicient to ignite spark plugs 18 and 19.

While we have described and illustrated one specific embodiment of our invention, it will be clear that variation-s of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spirit and scope of the invention as defined in the appended claims. For example, it is possible to utilize the system of the present invention with more than two magnetos. In such an instance, the A.C. output voltage of each magneto is coupled through a separate rectifying network to coil 31 of a relay having additional contacts similar to contact 24.

We claim:

1. A system for stopping an internal combustion engine system having plural magnetos and normally open condition responsive switch contacts in response to a malfunction, said malfunction being indicated by the closure of said normally open switch contacts to ground, comprising a relay having normally open contacts and a coil, a plurality of rectifying networks, means for connecting each of said magnetos in series circuit with said coil via a separate one of said rectifying networks so that the A.C. voltages deriving from said magnetos are supplied to said rectifying networks in an out of phase relationship, said rectifying networks including unidirectional conductor means poled such that the A.C. voltage deriving from the magneto with which it is connected is coupled to the coil only through the respective rectifying network, said series circuit further including said normally open switch contacts and leading to ground, and means connecting said magnetos to said normally open contacts of said relay and means connecting said normally open contacts to ground for short circuiting the AC. voltages deriving from said magnetos to ground in response to activation of said relay coil.

2. The system of claim 1 wherein each of said rectifying networks includes a diode as the unidirectional conductor and a resistance and capacitor, both in parallel with said diode, the values of said resistance and capacitance being selected so as to substantially damp transient variations and prevent destruction of the diode by the application of excess back bias voltage.

3. The system of claim 2 wherein the value of said resistors is on the order of 1,500 ohms and the value of said capacitor is on the order of 0.01 microfarad.

4. The system of claim 1 wherein said relay includes latch means for connecting said normally open contacts together after current flow through the coil has ceased.

5. A system for stopping an internal combustion engine having plural magnetos having a common ground comprising a condition responsive switch having normally open contacts,

a relay having normally open contacts and an actuator coil,

means electrically connecting a first of said normally open contacts of said condition responsive switch to a first end of said relay actuator coil and a second of said normally open contacts to ground,

a plurality of diode rectifying networks,

means separately connecting a plurality of said magnetos through individual diode rectifying networks to a second end of said relay actuator coil, said magnetos being separately connected to like electrodes of said diode rectifying networks, said relay actuator coil being connected to opposite electrodes of said diode rectifying networks for producing a single direct current voltage applied to said relay actuator coil,

means separately connecting said magnetos to said normally open relay contacts :for short circuiting the voltage output of said magnetos to ground in response to actuation of said relay contacts by said relay actuator coil when the first end of said relay actuator coil is gnound by the closing of the normally open condition responsive switch contacts.

6. The system of claim 5 wherein said relay further includes means for latching said contacts in a closed condition subsequent to the application of current to said coil.

7. The system of claim 5 further including a resistor connected across each of said diodes and a capacitor connected across each of said diodes, said resistor and capacitor having values selected so that transients deriving from said magneto are suppressed and excessive back bias voltages are not applied across the diodes in response to said transients.

8. The system of claim 5 wherein said relay has a plurality of electrically isolated normally open contacts, all of said relay contacts being electrically shorted together and grounded upon being actuated by said relay actuator coil.

References Cited by the Examiner UNITED STATES PATENTS 1,854,571 4/1932 Albertson 123146.5 X 2,276,636 3/1942 White 307--51 X 2,358,729 9/1944 Murphy 123-l46.5 X 2,443,060 6/1948 Wall 30710 X 2,467,333 4/1949 Murphy 123146.5 X 2,992,303 7/1961 Murphy 200-87 X MILTON O. HIRSHFIELD, Primary Examiner.

SAMUEL BERNSTEIN, STEPHEN W. CAPELLI,

Examiners.

R. V. LUPO, Assistant Examiner. 

1. A SYSTEM FOR STOPPING AN INTERNAL COMBUSTION ENGINE SYSTEM HAVING PLURAL MAGNETOS AND NORMALLY OPEN CONDITION RESPONSIVE SWITCH CONTACTS IN RESPONSE TO A MALFUNCTION, SAID MALFUNCTION BEING INDICATED BY THE CLOSURE OF SAID NORMALLY OPEN SWITCH CONTACTS TO GROUND, COMPRISING A RELAY HAVING NORMALLY OPEN CONTACTS AND A COIL, A PLURALITY OF RECTIFYING NETWORKS, MEANS FOR CONNECTNG EACH OF SAID MAGNETOS IN SERIES CIRCUIT WITH SAID COIL VIA A SEPARATE ONE OF SAID RECTIFYING NETWORKS SO THAT THE A.C. VOLTAGES DERIVING FROM SAID MAGNETOS ARE SUPPLIED TO SAID RECTIFYING NETWORKS IN AN OUT OF PHASE RELATIONSHIP, SAID RECTIFYING NETWORKS INCLUDING UNDIRECTIONAL CONDUCTOR MEANS POLED SUCH THAT THE A.C. VOLTAGE DERIVING FROM THE MAGNETO WITH WHICH IT IS CONNECTED IS COUPLED TO THE COIL ONLY THROUGH THE RESPECTIVE RECTIFYING NETWORK, SAID SERIES CIRCUIT FURTHER INCLUDING SAID NORMALLY OPEN SWITCH CONTACTS AND LEADING TO GROUND, AND MEANS CONNECTING SAID MAGNETOS TO SAID NORMALLY OPEN CONTACTS OF SAID RELAY AND MEANS CONNECTING SAID NORMALLY OPEN SWITCH CONTACTS AND LEADING TO GROUND A.C. VOLTAGES DERIVING FROM SAID MAGNETOS TO GROUND IN RESPONSE TO ACTIVATION OF SAID RELAY COIL. 